Drinking large quantities of fluid: This may cause you to urinate frequently, which you can possibly misinterpret as a pregnancy sign.
Kissing close family members:
...but kissing random strangers is fine and, in fact, to be encouraged.
Don´t test if you your boobs are sore every 5 minutes as they could get sore and that could be mistaken by a pregnancy sign
Don't eat anything you dont normally like in front of anyone else - they'll assume you're pregnant! (Damn tomato soup!)